In sawmills and other applications there is a need to elevate logs. In some applications it is desirable to singulate logs. For example, it may be desired to send logs one-by-one to a sawing system or other wood processing equipment. It is desirable that there be no interruption in the flow of logs to the wood processing equipment. The task of singulating logs would be easier if all logs were the same and all had an ideal log shape (for example, straight and cylindrical with a perfectly circular cross-section and a constant diameter). However, log singulating is made more difficult because real logs are neither all identical nor ideally shaped. Logs have different diameters. Some logs may taper significantly. Some logs may not be straight. Logs often have projecting bumps. In general, logs come in a variety of physical shapes, all of which are different from the ideal log shape.
Logs may be dirty. Bark or other debris may fall off of the logs. The accumulation of such debris can cause problems for some singulators.
It is desirable for a singulator to be able to take logs from a pile in which the logs may be skewed, crossed and/or tangled.
Another issue is that modern sawmills are expensive to construct and operate. It is desirable to operate saw mills and other log-processing operations efficiently. Thus, there is commercial pressure for log singulators and other log-handling and log-processing equipment that can operate reliably and at relatively high speeds.
Various log singulators are currently used. Two main categories of log singulators are “arm-type” singulators and “all-live-surface” singulators. Arm-type singulators have a series of arms arranged to lift logs past a set of fixed members. In all-live-surface singulators all of the surfaces that contact the logs can move. Rotary log feeders are an example type of all-live-surface singulators.
All live surface step/wave log singulators are used worldwide. Such singulators have a number of steps that are reciprocated up and down to elevate logs from a pile to a conveyor. Each step is designed to carry only a single log. If a step picks up two logs it is intended that one of the logs will fall off before being delivered to the conveyor.
Step sorter log singulators move logs along a series of steps which are distributed horizontally along an incline. U.S. Pat. No. 5,423,417 (“Log Ladder”) describes one example of a step sorter singulator. “Double Acting Step Sorter” singulators, are described for example in U.S. Pat. No. 6,450,324 (“Double Acting Log Singulator”), U.S. Pat. No. 5,374,157 (“Apparatus for moving Sawlogs”), Canadian Patent No. 2271931 (“Conveyor Apparatus”), and Canadian Patent No. 2270484 (“Article Transfer Device”). Single Acting Step sorter singulators, are described for example in U.S. Pat. No. 5,257,688 (“Step Feeder”), U.S. Pat. No. 5,174,351 (“Step Feeder”), U.S. Pat. No. 5,351,729 (“Log Unscrambling Device), Canadian Patent No. 2270484 (“Article Transfer Device”), Canadian Patent No. 2271931 (“Conveyor Apparatus”) and Canadian Patent No. 2074645 (“Separator for Saw Logs”).
“Rotary sorter” singulators, as described for example in U.S. Pat. No. 5,011,024 (“Rotary Log Sorter”), have drums with pockets or arms that rotate continuously. The pockets or arms carry logs to an out-feed conveyor. U.S. Pat. No. 4,930,616 describes a rotary log singulator having longitudinal drums containing pockets, plus a lifting and separating bar.
U.S. Pat. No. 5,119,930 (“Quadrant Log Feeder”) describes an oscillating quadrant/arc singulator which elevates logs along a curved surface. U.S. Pat. No. 6,637,581 (“Vertical Log Singulator with Profiled Surface”) describes a two-stage oscillating singulator.
Singulators that are in current use (including many singulators of types as described above) typically suffer from one or more problems that impair their effectiveness. Examples of such problems include:                A singulator may deliver two logs at the same time onto a take-away conveyor under some circumstances.        A log rejected by a singulator after the log has been elevated may knock other lower logs off of the singulator, thereby causing lost productivity.        A singulator may not be amenable to operation at higher speeds.        A singulator may not be energy efficient.        A singulator may be difficult to maintain.        A singulator may occupy too much horizontal space.        A singulator may not be able to provide a desired elevation gain.        A singulator may not work well with a deeper pile of logs on an infeed log deck.        A singulator may be difficult and/or costly to install.        It may be difficult and/or costly to provide a way to remove debris from a singulator.        A singulator may not be easily installed in place of an existing singulator without significant modification to the site.        
There is therefore a need for log singulators and log elevators that avoid or reduce disadvantages of currently-available log singulators. There is a general need for log singulators and log elevators that provide alternatives to those currently available in the market. There is a particular need for log singulators and log elevators that can be configured to fit into varying sawmill circumstances and production requirements.